1. Field of the Invention
The invention concerns a grip arranged movably on a pull shaft of a crystal pulling system whereby the grip has a slide ring which can be moved on the pull shaft and on which grip arms which can swivel beneath a thickening of a crystal ingot are borne so as to swivel around a swivel bearing, each of which grip arm has a holding jaw for grasping below the thickening of the crystal ingot and for which each grip arm has an outwardly directed activating arm, at the free end of which a cable of a cable drum arranged above the grip acts.
2. Description of the Related Art
A grip of the above type is the object of U.S. Pat. No. 5,126,113 to Yamagishi et al. In the grip explained in said publication, the respective holding jaws grip into a necking of the crystal ingot at approximately a vertical line below the swivel bearing of their grip arms. As a result of the weight of the crystal ingot, the holding jaws have a tendency to move radially outward and as a result to release the crystal ingot. In order to pull the crystal, the pull shaft and the grip are moved upward synchronously. If the grip were moved upward more sharply than was the pull shaft, the grip arms would have the tendency to move into open position.
To prevent an unintended opening of the grip aims, the grip arms according to said U.S. Pat. No. 5,126,113 to Yamagishi et al. in closed position are enclosed by an axially movable ring. During the closing movement of the grip arms, this ring slips from the upper position down onto the grip arms and then prevents the opening of the grip alms. Opening is not possible until the ring is pushed upward manually. The grip according to U.S. Pat. No. 5,126,113 to Yamagishi et al. therefore does not permit automatic opening and closing of its grip arms. In addition, there is a danger with it that the ring will tip on the grip arms as they are closed and therefore will not come into its lower position in which it blocks the grip arms in closed position.
The invention is based on the problem of configuring a grip of the type described above such that it can be moved only through the drive of the cable drums into open and closed position and cannot come into an open position on its own.
This problem is solved according to the invention in that the grip arms cross each other, that the holding jaw of each grip arm is arranged at the side of the crystal ingot lying across from the swivel bearing of the particular grip arm, and the activating arm is situated at the side of the grip arm across from the swivel bearing.
In such a grip, the weight of the crystal ingot gripped causes the grip to be acted upon by force in the closed position. A self-activated opening of the grip is automatically prevented by this means without an additional safety device. As a result of the crossing of the grip arms, one can select the effective lever arm for the closing force large enough so that the forces which must be applied via the cable cannot result in an unintentional opening of the grip. An opening of the grip is not possible until the crystal ingot is supported and therefore its weight no longer acts on the grip.
The grip is especially simply configured if a total of two grip arms situated opposite each other are provided.
The thickening of the crystal ingot is supported by the holding jaws from below on all sides if according to another further development of the invention the one holding jaw has a holding grove which is open on one side and is configured for grasping over a crystal neck of the crystal ingot and the other holding jaw has a holding ridge which engages in the holding groove in closed position and there can rest against the crystal neck.
The holding jaws of the grip do not have to move during opening and closing on a radius around the particular swivel bearing of the particular grip arm, but rather they can execute the radial lift to the outside or inside at an elevation if according to another, particularly advantageous further development of the invention the swivel bearings of the grip arms each are provided on shackles which are provided so as to swivel around an axis aligned parallel with the swivel axis of the swivel bearing and are aligned swivelably on the sliding ring radially to the outside.
As the grip is pulled up on the pull shaft by means of the cable, the swivel movement of the grip arm is limited if the shackles each have a stop which limits the swivel movement of the grip arm linked to it in open position.
The stop is particularly simply configured if it is provided on a downward-directed extension arm of the particular shackle. During the raising of the pull shaft, the cables always remain sufficiently tight so that no slack develops if the cable drums are configured as electrical springs.
The invention permits various embodiments. For further illumination of its basic principle, one such embodiment form is depicted in the drawings and will be described below.